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How Plants Fight Freezing

Plants can't put on sweaters or head south when the air gets chilly, but many can increase their tolerance to freezing. Researchers seeking to enhance this trait are asking how plants sense the cold and what they do to increase their resistance. Now a team provides a preliminary answer by cloning, for the first time, a gene involved in sensing and responding to low temperatures.

Plants brace themselves for cold weather by setting off a chain of gene activations that protects their cells; this response keeps cell membranes fluid and flexible, for example. Plant biologists Jian-Kang Zhu, Hojoung Lee, and colleagues at the University of Arizona, Tucson, suspected the existence of a regulator gene that helps control this process before they worked out the gene's sequence. In a 1998 study they identified a relevant mutant of the model plant, Arabidopsis thaliana. The mutant was unusually sensitive to cold but responded normally to other stressors. The team surmised that the plant must be missing a gene normally responsible for keeping the cold response in check. They dubbed this presumed regulator HOS1.

Now the same team reports that they have located the HOS1 gene and worked out its sequence. The research yielded a clue about how HOS1 might work, the researchers report in the April issue of Genes and Development. Part of the protein encoded by HOS1 closely resembles the so-called RING finger proteins. Some of these proteins tell cells which proteins to degrade and which to spare. It's not clear yet whether the HOS1 protein acts the same way, but if it does, it may degrade a protein that switches on cold-responsive genes, thereby dampening the plant's sensitivity to cold, according to Lee.

"Zhu and colleagues have provided an important component of the wiring diagram for low-temperature signaling," says molecular geneticist Michael Thomashow at Michigan State University, East Lansing. "It's an early step, but one day this information may help to enhance cold tolerance in crops."